(a) Technical Field
The present disclosure relates generally to an apparatus and method for guiding a driver in coasting of a vehicle. More particularly, the present disclosure relates to an apparatus and method for guiding a driver to coasting in eco-friendly vehicles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and fuel cell electric vehicles (FCEVs).
(b) Background Art
Internal combustion engine vehicles using fossil fuels, such as gasoline and diesel, have a variety of limitations such as environmental contamination caused by the engine exhaust, global warming caused by carbon dioxide emissions, and respiratory illnesses caused by creation of the ozone. Accordingly, newer vehicles have been developed, including vehicles driven by electric power i.e., eco-friendly vehicles such as electric vehicles (EVs) driven by a motor, hybrid electric vehicles (HEVs) driven by an engine and a motor, and fuel cell electric vehicles (FCEVs) driven by a motor powered by electricity generated from fuel cells.
In such eco-friendly vehicles, during the braking or coasting by inertia, regenerative braking (RB) is performed in which the vehicle's inertial energy is recovered through a motor's electricity generation operation to charge batteries (i.e., motor charging). Particularly, when a driver recognizes the need to slow down due to events such as an crossroad, traffic lights, a curved road, nearby vehicles, or other obstacles appearing ahead of the vehicle (i.e., a deceleration event), and takes his/her foot off the accelerator pedal, it is possible to recover energy through the vehicle's coasting control, i.e., the motor torque control, that performs electric generation.
As is well-known in the art, when a driver of an eco-friendly vehicle removes his/her foot from the brake pedal and the accelerator pedal during deceleration of the vehicle, coasting is performed. In this case, the vehicle is decelerated through coasting torque (i.e., negative torque) control on the motor, and energy simultaneously recovered by the motor is stored in batteries.
Here, “Pedal off” means a state in which a driver does not apply or releases the relevant pedal, while “Pedal on”, on the other hand, means a state in which the driver applies the relevant pedal. Thus, in an eco-friendly vehicle, vehicle energy is recovered and converted to electric energy using a motor during the braking or coasting, and the recovered electric energy is stored in batteries so as to be reused for driving the motor, thereby enabling increase of mileage (i.e., driving distance), improvement of the fuel efficiency, and efficient use of energy.
FIG. 1 is a graph illustrating a typical deceleration pattern of a driver. Most drivers take their foot off the accelerator pedal and then step on the brake pedal to decelerate a vehicle from the current speed to the target speed via the brake (i.e., frictional braking unit) when a deceleration event exists at the front side of a vehicle. In this case, drivers determine the timing to take his/her foot off the accelerator pedal and the timing to step on the brake pedal using their eyes. In reality, most drivers take their foot off the accelerator pedal later than appropriate timing for pedal-off and rush to step on the brake pedal for deceleration of the vehicle. Such deceleration suffers disadvantages in terms of mileage and fuel efficiency, as compared to deceleration only by coasting.
On the other hand, in cases of eco-friendly vehicles such as electric, hybrid and fuel cell vehicles, since it is possible to control torque over the drive motors, i.e., a motor for driving the vehicles, the vehicles are able to realize deceleration through torque control (i.e., coasting torque control) on the drive motor while coasting, which is similar to the deceleration of an internal combustion engine vehicle equipped with an automatic transmission. When a driver takes his/her foot off the accelerator pedal at an appropriate time after the driver recognizes a deceleration event in advance, without working on a brake pedal, the driver can reduce the speed of the vehicle smoothly down to a target speed through motor torque control. When a vehicle is decelerated by operating on the brake pedal, not only by coasting, since the total braking force is secured by distribution between frictional braking from the brake and regenerative braking from the motor, energy recovery is performed while being limited only to distributed regenerative braking, causing a disadvantage in increasing mileage and improving fuel efficiency.
Accordingly, it is advantageous to decelerate a vehicle from a current speed down to a target speed only through coasting without the operation of a brake, if possible. Furthermore, in case of eco-friendly vehicles, the deceleration force of a vehicle can be controlled by varying the torque of a drive motor during the coasting.
When drivers take advantage of such deceleration force adjustment by use of the drive motor while coasting a vehicle with accelerator and brake pedal off, i.e., without use of a brake operation and using only the vehicle's natural friction, drivers can reduce the speed down to a target speed at a desired location. Accordingly, the mileage and the fuel efficiency are improved moreso when a driver takes the foot off the accelerator pedal at an appropriate timing and then puts on the brake versus taking off the foot later. There is also an advantage in that replacement of consumable parts in the brake system may be extended.
Therefore, it is advantageous for mileage increase and fuel efficiency improvement in eco-friendly vehicles to be able to make the most of deceleration through coasting without brake operation while reducing the speed from a current speed to a target speed. For this, appropriate coasting torque control over a drive motor is required. A function for guiding and inducing a driver into coasting by taking his/her foot off the accelerator pedal at an appropriate timing is also needed.
In this regard, FIG. 2 is a graph illustrating a typical coasting inducible and guidable section. When a driver intends to reduce the current vehicle speed to the target speed, there is a speed difference at a location of a deceleration event where deceleration of a vehicle needs to be completed when a driver differentiates the accelerator pedal-off timing based on an optimal pedal-off timing. Particularly, since adjustment of the engine drag is impossible, it is difficult for an internal combustion engine vehicle to set and control deceleration of the vehicle in a desired speed profile.
Accordingly, since the internal combustion engine vehicle can only reduce the speed in a uniform speed profile form, as shown in FIG. 2, it is difficult for the vehicle to guide (at the accelerator pedal-off point) and induce a driver into coasting such that the speed of the vehicle at the location of a deceleration event falls within the final speed allowable error. That is, it is difficult to induce the driver into coasting such that the vehicle can be decelerated according to a speed profile between the maximum and minimum limits by setting the maximum and minimum limits of the coasting speed profile based on the final speed allowable error.
Notably, time (i.e., coasting guide section in FIG. 2) for guiding a driver to the timing for coasting (i.e., accelerator pedal-off timing) is relatively short (see time interval for guiding coasting as shown in FIG. 2). When a driver cannot recognize an appropriate accelerator pedal-off point during the short time period within the final speed allowable error, coasting becomes impossible. Even when a guide function is provided, the function does not operate if the appropriate timing is missed.
On the other hand, in an eco-friendly vehicle, the speed profile for deceleration of a vehicle can be controlled within the final speed allowable error through a coasting torque control on the drive motor. Thus, even with the final speed allowable error of the final speed set constant, it is possible to extend the time period for guiding a driver to coasting. However, there is little research so far on the technology that allows a driver of an eco-friendly vehicle to be guided and induced into coasting at an appropriate timing in accordance with driving situations such that eco-driving can be realized through energy recovery. Consequently, drivers do not recognize the timing for coasting, and coasting is thus not performed at an appropriate timing in spite of a situation where coasting may be possible. This makes it difficult to recover energy, increase the mileage, and improve the fuel efficiency through coasting.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure, and therefore, it may contain information that does not form the related art that is already known to a person of ordinary skill in the art.